Method and apparatus for selection of linear combination coefficients for precoding in frequency-selective channels

Abstract

The disclosure provides a method of providing implicit channel state information (CSI) feedback from a user equipment (UE). The method includes determining a precoding matrix indicator (PMI) selection decision metric, selecting one of a sub-band (SB) linear combination coefficient (LCC) selection method, a wideband (WB) LCC selection method, or a sub-band group (SBG) LCC selection method, based on the determined PMI selection decision metric, determining, using the selected LCC selection method, PMI indices based on sub-bands configured by a base station, and transmitting the determined PMI indices to the base station.

What is claimed is: 
     
       1. A method performed by a user equipment (UE), the method comprising:
 determining a precoding matrix indicator (PMI) selection decision metric; 
 selecting one of a sub-band (SB) linear combination coefficient (LCC) selection method, a wideband (WB) LCC selection method, or a sub-band group (SBG) LCC selection method, based on the determined PMI selection decision metric; 
 determining, using the selected LCC selection method, PMI indices based on sub-bands configured by a base station; and 
 transmitting the determined PMI indices to the base station. 
 
     
     
       2. The method of  claim 1 , wherein the determined PMI selection decision metric includes a ratio between LCC energy after frequency domain (FD) compression and LCC energy before FD compression. 
     
     
       3. The method of  claim 2 , wherein selecting one of the SB LCC selection method, the WB LCC selection method, or the SBG LCC selection method comprises:
 comparing the ratio with a threshold; 
 selecting the SB LCC selection method, in response to the ratio being greater than the threshold; and 
 selecting one of the WB LCC selection method or the SBG LCC selection method, in response to the ratio being less than or equal to the threshold. 
 
     
     
       4. The method of  claim 3 , wherein selecting one of the WB LCC selection method or the SBG LCC selection method comprises selecting the SBG LCC selection method, in response to an SB grouping achieving lossless compression. 
     
     
       5. The method of  claim 3 , wherein selecting one of the WB LCC selection method or the SBG LCC selection method comprises:
 determining a number of the sub-bands configured by the base station and a maximum number of sub-bands; and 
 selecting one of the WB LCC selection method or the SBG LCC selection method, based on a comparison of the number of the sub-bands configured by the base station and the maximum number of sub-bands, and whether the number of the sub-bands configured by the base station is odd or even. 
 
     
     
       6. The method of  claim 5 , wherein selecting one of the WB LCC selection method or the SBG LCC selection method, based on the comparison of the number of the sub-bands configured by the base station and the maximum number of sub-bands, and whether the number of the sub-bands configured by the base station is odd or even comprises:
 selecting the SBG LCC selection method, in response to the number of the sub-bands configured by the base station being less than the maximum number of sub-bands, and the number of the sub-bands configured by the base station being even; and 
 selecting the WB LCC selection method, in response to the number of the sub-bands configured by the base station being greater than or equal to the maximum number of sub-bands, or the number of the sub-bands configured by the base station being odd. 
 
     
     
       7. The method of  claim 1 , wherein the determined PMI selection decision metric includes an average capacity difference. 
     
     
       8. The method of  claim 7 , wherein selecting one of the SB LCC selection method, the WB LCC selection method, or the SBG LCC selection method comprises:
 selecting the SB LCC selection method, in response to the average capacity difference being greater than 0; and 
 selecting one of the WB LCC selection method or the SBG LCC selection method, in response to the average capacity difference being less than or equal to 0. 
 
     
     
       9. The method of  claim 8 , wherein selecting one of the WB LCC selection method or the SBG LCC selection comprises selecting the SBG LCC selection method, in response to an SB grouping achieving lossless compression. 
     
     
       10. The method of  claim 8 , wherein selecting one of the WB LCC selection method or the SBG LCC selection method comprises:
 determining a number of the sub-bands configured by the base station and a maximum number of sub-bands; and 
 selecting one of the WB LCC selection method or the SBG LCC selection method, based on a comparison of the number of the sub-bands configured by the base station and the maximum number of sub-bands, and whether the number of the sub-bands configured by the base station is odd or even. 
 
     
     
       11. The method of  claim 10 , wherein selecting one of the WB LCC selection method or the SBG LCC selection method, based on the comparison of the number of the sub-bands configured by the base station and the maximum number of sub-bands, and whether the number of the sub-bands configured by the base station is odd or even comprises:
 selecting the SBG LCC selection method, in response to the number of the sub-bands configured by the base station being less than the maximum number of sub-bands, and the number of the sub-bands configured by the base station being even; and 
 selecting the WB LCC selection method, in response to the number of the sub-bands configured by the base station being greater than or equal to the maximum number of sub-bands, or the number of the sub-bands configured by the base station being odd. 
 
     
     
       12. The method of  claim 1 , wherein the WB LCC selection method comprises:
 determining a single LCC matrix for an entire band; and 
 mapping the single matrix to PMI indices corresponding the SB LCC selection method. 
 
     
     
       13. The method of  claim 1 , wherein the SBG LCC selection method comprises:
 determining a set of LCC matrices, wherein a total number of matrices included in the set of the LCC matrices is less than a number of discrete Fourier transform (DFT) components utilized in the SB LCC selection method; and 
 mapping the set of LCC matrices to PMI indices corresponding the SB LCC selection method. 
 
     
     
       14. A user equipment (UE), comprising:
 a transceiver; and 
 a processor configured to:
 determine a precoding matrix indicator (PMI) selection decision metric, 
 select one of a sub-band (SB) linear combination coefficient (LCC) selection method, a wideband (WB) LCC selection method, or a sub-band group (SBG) LCC selection method, based on the determined PMI selection decision metric, 
 determine, using the selected LCC selection method, PMI indices based on sub-bands configured by a base station; and 
 transmit, via the transceiver, the determined PMI indices to the base station. 
 
 
     
     
       15. The UE of  claim 14 , wherein the determined PMI selection decision metric includes a ratio between LCC energy after frequency domain (FD) compression and LCC energy before FD compression. 
     
     
       16. The UE of  claim 15 , wherein the processor is further configured to:
 compare the ratio with a threshold, 
 select the SB LCC selection method, in response to the ratio being greater than the threshold, and 
 select one of the WB LCC selection method or the SBG LCC selection method, in response to the ratio being less than or equal to the threshold. 
 
     
     
       17. The UE of  claim 16 , wherein the processor is further configured to select the SBG LCC selection method, in response to an SB grouping achieving lossless compression. 
     
     
       18. The UE of  claim 16 , wherein the processor is further configured to:
 determine a number of the sub-bands configured by the base station and a maximum number of sub-bands, and 
 select one of the WB LCC selection method or the SBG LCC selection method, based on a comparison of the number of the sub-bands configured by the base station and the maximum number of sub-bands, and whether the number of the sub-bands configured by the base station is odd or even. 
 
     
     
       19. The UE of  claim 18 , wherein the processor is further configured to:
 select the SBG LCC selection method, in response to the number of the sub-bands configured by the base station being less than the maximum number of sub-bands, and the number of the sub-bands configured by the base station being even; and 
 select the WB LCC selection method, in response to the number of the sub-bands configured by the base station being greater than or equal to the maximum number of sub-bands, or the number of the sub-bands configured by the base station being odd. 
 
     
     
       20. The UE of  claim 14 , wherein the determined PMI selection decision metric includes an average capacity difference. 
     
     
       21. The UE of  claim 20 , wherein the processor is further configured to:
 select the SB LCC selection method, in response to the average capacity difference being greater than 0; and 
 select one of the WB LCC selection method or the SBG LCC selection method, in response to the average capacity difference being less than or equal to 0. 
 
     
     
       22. The UE of  claim 21 , wherein the processor is further configured to select the SBG LCC selection method, in response to an SB grouping achieving lossless compression. 
     
     
       23. The UE of  claim 21 , wherein the processor is further configured to:
 determine a number of the sub-bands configured by the base station and a maximum number of sub-bands, and 
 select one of the WB LCC selection method or the SBG LCC selection method, based on a comparison of the number of the sub-bands configured by the base station and the maximum number of sub-bands, and whether the number of the sub-bands configured by the base station is odd or even. 
 
     
     
       24. The UE of  claim 23 , wherein the processor is further configured to:
 select the SBG LCC selection method, in response to the number of the sub-bands configured by the base station being less than the maximum number of sub-bands, and the number of the sub-bands configured by the base station being even; and 
 select the WB LCC selection method, in response to the number of the sub-bands configured by the base station being greater than or equal to the maximum number of sub-bands, or the number of the sub-bands configured by the base station being odd. 
 
     
     
       25. The UE of  claim 14 , wherein the WB LCC selection method comprises:
 determining a single LCC matrix for an entire band; and 
 mapping the single matrix to PMI indices corresponding the SB LCC selection method. 
 
     
     
       26. The UE of  claim 14 , wherein the SBG LCC selection method comprises:
 determining a set of LCC matrices, wherein a total number of matrices included in the set of the LCC matrices is less than a number of discrete Fourier transform (DFT) components utilized in the SB LCC selection method; and 
 mapping the set of LCC matrices to PMI indices corresponding the SB LCC selection method.